thèse doctorat de l'université bordeaux 2 - ISPED-Enseignement à ...

2.4 Multiple factors involved in traffic crashesRTCs are usually consequences of multiple factors [49]. Two studies, conductedindependently in the United States and Great Britain, showed that although road user-relatedfactors were identified in up to 94% of RTCs, other factors were also involved in a third ofthem (Figure 3) [55]. In most cases, such crashes resulted when both road user- and roadsituational factors (indicated in red) were involved. These situational factors can be fixed roadenvironmental characteristics, such as road geometry, or transient environmentalcircumstances, such as weather, light, or traffic conditions [55]. Current evidence alsosuggests that interventions on road environment-related factors can prevent driver-relatederrors and violations, the foremost cause of traffic crashes reported elsewhere [58]. In thisregard, the two known approaches are to make roads “self-explaining” and “forgiving” [3].For instance, speeding is clearly facilitated by plain road profile and installation of speedcalmingmeasures in such situations decreases crash likelihood by indirectly influencingdrivers to reduce their speeds (self-explaining roads) [11]. Further, installation of impactabsorbing barriers would mitigate the severity of crash if the crash occurs at all (forgivingroads) [14].Figure 3. Contribution of risk factors in road traffic crashes (adapted from [55])Great BritainUnited States of AmericaRoad andenvironment28%Vehicle8%Road andenvironment34%Vehicle12%2 123 12241427366567Road User94%Road user93%2.5 Implications of interactions for highway safetyHighways are the backbone of the economy in all countries. In absence of effective railwaysand motorways, mixed dual- and single-roads are the major link for almost all transportationof consumables from farms to markets [6]. These roads are over-involved in crash fatalities.For instance in the United States of America (USA), 54% of traffic fatalities occur on suchtype of road sections [59], similarly, interurban road sections in France account for one thirdof road crashes but two thirds of road fatalities (Table 2) [9]. Undoubtedly, severity of trafficcrashes on these roads is higher than those on urban roads. The key determinant of the highcrash fatality is travel speed, itself allowed on these road types [19, 24]. Relationship between16